immune system

• An overview of the immune system in vertebrates

  
• Understand contexts in which the immune system does (e.g. vaccines) and doesn't (e.g. allergies and autoimmune diseases) work

  
• Immune system


  Body's defense system

  
• How the immune system works


  1. Innate immunity

  2. Barrier defenses: skin, mucous, tears, etc.

  3. Internal defenses: phagocytic cells, inflammatory response

  4. Adaptive (acquired) immunity

  5. Humoral response: B cells and antibodies

  6. Cellular response: T cells

  
• Why the immune response (not) work


  • Immunological memory
  • Vaccines
  • Allergies, autoimmunity, immunodeficiency

  
• Inflammatory response


  • Local vs. systemic (e.g. fever)
  • Mast cells release histamines
  • Macrophages release cytokines
  • Phagocytic cells include macrophages localized in certain body tissues and neutrophils that circulate in the bloodstream

  
• Antimicrobial peptides target pathogens
• Accumulation of pus - fluid rich in white blood cells, dead pathogens, and cell debris
• Adaptive immunity


  • Relies on two types of lymphocytes
  • Humoral (antibody-mediated) response - B-cells
  • Cell-mediated response - T-cells
  • Antigen receptors - Every lymphocyte has one type of antigen receptor, you have millions of lymphocytes each with a different type of receptor

  
• 1. cell action


  1. Antigen: any substance on or secreted by a pathogen that can elicit an immune response

  2. B-cells that can bind the antigen proliferate (clonal selection)

  3. Effector cells (plasma cells) produce antibodies

  4. Memory cells

  
• Antibodies


  • Prevent infection (neutralization)
  • Tag foreign bodies for phagocytosis (opsonization)

  
• 1. cell action


  1. T-cells recognize antigen fragments presented by host cell

  2. Host proteins called major histocompatibility complexes (MHC) present antigen fragments on the cell surface for recognition

  3. Helper T-cells that can bind the fragment proliferate (clonal selection)

  4. Promote proliferation of appropriate B-cells

  5. Signal cytotoxic T-cells to kill the infected host cells

  6. Memory T-cells

  
• Why adaptive immunity is so powerful


  • Diversity of antigen receptors
  • Self-tolerance
  • B and T cells proliferate after activation
  • Immunological memory

  
• Diversity of antigen receptors


  • There are millions of different kinds of B-cells and T-cells, each with a different type of antigen receptor
  • Gene rearrangement
  • Self-reactive lymphocytes undergo apoptosis

  
• Vaccination and immunization


  Vaccine: nonpathogenic form of a microbe or part of a microbe (or the mRNA instructions for it) elicits an immune response and immunological memory

  
• Examples of vaccines


  • Smallpox
  • Chicken pox
  • Hepatitis
  • Influenza
  • Measles
  • Mumps
  • Polio
  • Pertussis (whooping cough)
  • Tetanus
  • Covid-19
• When the immune response doesn't work

  • Immune rejection - Blood transfusion (A, B & O), Organ transplants
  • Exaggerated response - Allergies
  • Self-directed response - Rheumatoid arthritis, Lupus, Multiple sclerosis
  • Diminished response - Stress, age, lack of sleep, Antigenic variation, Viral latency